Mass spectrometer



Jan. 29, 1952 C BERRY 2,583,541

MASS SPECTROMETER Filed May 17, 1948 F/Gi FIG. 3.

INV NTO CLIFFORD E. 55!? O ATTORNEY Patented Jan. 29, 1952 MASS SPECTROMETER Clifford E. Berry, Pasadena, Calif., assignor to Consolidated Engineering Corporation, Pasadena, Calif., a corporation of California Application May 17, 1948, Serial No. 27,513

18 Claims. 1

This invention is concerned with mass spectrometers and particularly with improvements therein adapted to facilitate analysis of certain substances such as alcohols, aldehydes, ketones, etc. These improvements take the form of novel sample introducing means or leaks, as they are referred to in the art, which function to make possible analyses which have heretofore been diflicult or impossible to perform.

A mass spectrometer is an apparatus employed for sorting ions. Ordinarily it includes an ionization chamber in which molecules of a material to be analyzed are bombarded by a stream of electrons and thereby converted into ions. These ions are propelled, from the ionization chamber, into and through an analyzer chamber where they are subjected to a magnetic or electrical field force or both. In the analyzer chamber, under the influence of the field forces, the ions are segregated into a plurality of diverging ion beams having difierent specific masses, with each beam being composed of ions of the same specific mass. The diverging beams are successively focused on and discharged at an ion collector. The current thus produced from each ion beam is indicative of the amount of ions in that beam, and may be a measure of the partial pressure of the molecules (from which the ions were derived) present in the material undergoing analySlS.

capillary leak through which the sample flows from the source into a gas inlet tube connected to an inlet nipple which forms a part of the ionization chamber. The so-called leak is generally designed so that the gas flow therethrough, at the subsisting pressures, will be by molecular diffusion rather than viscous flow. This is necessary to correspond to the character of the gas flow from the ionization chamber into the analyzer chamber which flow is also by molecular diffusion.

Heretofore it has been virtually impossible to analyze certain substances such as alcohols, ketones, aldehydes, and other oxygenated compounds with the mass spectrometer. This disability is a result of the strong adsorptive eifects of these substances in the system, which impedes removal of used samples and causes cross contamination.

I have now found that the major portion of the deleterious adsorption occurs in the length of tubing that connects the sample leak with the ionization chamber. Accordingly I have developed a leak which maybe placed either in the ionization chamber itself, or immediately adja- The ionization chamber and the analyzer chamber are normally operated at a low pressure on the order of 0.1 and .001 micron respectively so that the mean free path of the ions is sufficiently large compared to the physical dimensions of the apparatus that collisions of the ions with neutral molecules will not scatter the ions and interfere with sharp focusing of beams.

Conveniently, the required low pressures are obtained by enclosing the ionization chamber and the analyzer chamber in a sealed envelope and evacuating the envelope through a conduit connected to an evacuating system. Various types of vacuum pumps, such as diffusion pumps or molecular pumps or combinations thereof that are capable of accomplishing this high degree of evacuation may be employed and are well known. Since the pressure of the sample to be analyzed is generally considerably greater than that obtaining in the ionization and analyzer chambers,

it is necessary to provide means forreducing the sample pressure as it is admitted to the ionization chamber without disturbing the abundance ratio of the components in the sample. This is generally accomplished by means of a leak or 'cent to the chamber so as to appreciably minimize the effects of this undesirable adsorption. Additionally I have found that objectionable adsorption on the solid surfaces intermediate the leak and the ionization chamber proper is less pronounced when these solid surfaces are metal than when they are glass. The invention is therefore additionally directed to the reduction or elimination of exposed glass surfaces between the leak and the chamber.

The invention contemplates in the analysis by mass spectrometry of gaseous mixtures containing one or more oxygenated organic compounds, the improvement which comprises admitting the sample substantially directly into the ionization chamber through a capillary leak. Additionally the invention contemplates in a mass spectrometer, the combination which comprises an ionization chamber and a capillary leak for introducing gas substantially directly into the ionization chamber. Preferably any exposed solid surfaces between the leak and the chamber are metal.

In accordance with one embodiment of the invention, I provide a glass tube, one end of which is adapted to slip over the inlet nipple of a conventional mass spectrometer ionization chamber. Within the bore of the glass tube is sealed a perforated metal foil transversely thereto and adjacent to the end of the tube which is to he slipped over the ionization chamber.

Inanother embodiment of the invention, I provide a leak which is adapted to be inserted in the ionization chamber nipple and which comprises a tubular metal body having a longitudinal bore. One end of the bore is enlarged so as to form a shoulder within the body and a perforated metal foil is placed transversely to the bore the invention are suitable for use in conjunction with an evacuated chamber of anytype" of'apparatus wherein proximity of thesam'ple leak to the chamber is a desirable feature.

The invention will be more clearly understood by reierenceto the following detailed discussion thereof, taken in relation to the' accompanying drawing in which: I I I I Fig. 1 is an elevation view of the'ioniz'ation chamber end of a mass spectrometer and a leak in accordance with one embodiment of the 'invention;

Fig. 2 is a section taken on the line2'-2 of -L nd Fig.3 is a sectional elevation of a leak in accordance with another embodiment of the invention disposedin an inlet nipple as for example associated with an ionization chamber.

Referring to Figs. 1 and 2, a conventional mass spectrometer includes an envelope I0, an analyzer tube l2, and an I ionization chamber l3 all of which elements have been described in detail above. An ionization chamber, "which in itself forms no part oi the present invention, generally includes an inlet nipple l4. I I

In the drawing, I have shown one embodiment ,of the inventionassociated with the inlet nipple M. This leak comprises a thickwalled glass tube lfihavinga longitudinal bore 11 and adapted to slip over the outer end of the inlet nipple 14. Adjacent that end of the tube l'fiwhichis to be inserted over theinlet nipple 14,1 provide a transverse perforated disk 18 which is I convem'ently a metal foil disk sealed into 'the glass itself. In the drawing, the tube I5 'is shown enlarged at IBA, the enlarged portion havin the disk l8 sealed therein.

The feature of the invention "which permits a mass spectrometer to be used 'for the analysis of alcohols andother oxygenated compounds is the proximity of the leak, i. e. the disk 18,120

the ionization chamber I3. It will be seen irom an examination of the drawing that they exposed surfaces intermediate the leak 18 and the ionization chamber are reduced to'a minimum by virtue of the construction of the leak of the invention.

The disk 18 which is conveniently metal 'foil and preferably gold foil, is designed in accordance with the operating pressures andthe sample volumesrequired. Thus the size of holes 20 in the disk will be determined bythe pressures employed and generally will have a diameter approximately of the mean free path of the sample molecules at the pressure subsisting at 4 the inlet side of the perforated disk; i. e." at the Side of the disk remote from the ionization -chainher. It is necessary that the gas sample flow through the leak by molecular diffusion rather than by viscous flow. For this reason it is important that the perforations in the leak be of smaller diameter and preferably of a diameter of about 1 6 that of the mean free path of the molecules. I I I I The volume of gas necessary foropiaration of the instrument will govern the number of holes (of a size determined by the operating pressure) 'which should be formed in the metal disk. The size of the instrument and particularly the size I of the ionization chamber will determine the vol ume of gas required. As an example, an inlet system under pressure of about 0.3 mm. of merholes.

Another embodiment ofthe'invention is shown in sectional elevation in Fig. 3. Inthisfiigure the leak is inserted in a' nipple l4,- forex'am'ple of'the ionization chamber of Fig, 11 which isconnected' to thefjsample' source through a'tube'22,

one end of which "fits over: the nipple 14. The

le'ak shown in FigJScOm'prises a metal bodyigfl preferably cylindricahin shape 'andhaving "an elongated "bore25 therethrough. I The bore" 25 is formed in two sections 25A, 25B,"the latter bein generally'shorter and of larger di'ameterthan'the section 25A, Ametal foil leak" 28 such "as that described with "relation to "Figs 'l' 'and' 2 is "finserted transversely 'in*'the bore '25 ofthe body 24 so as to 'abutagainsta'shoulder 121 'formed between the small and largesections'fiA; 25B,

' respectively of the bore. A metal 's1eeve'30 hav- 'ing' a bore 3| of substantially the same diameter as the section 25A of thebore 25 is insertedin the large "section 25B of the bore 125 sons-to hold the 'foil 28Ta'gainst the shoulder 21.

The "form of 'l'eak'as'shown in Fig. 3 is adapted 'to insertion inlthe nipple of theioniza'tion'cham- .ber itself bringing the sample leak substantially within the confines "of the chamber and reducing the adsorptive surfaces between'thel'eak and'the chamber to an absolute minimum. I

I Theimproved leak of theinvention was developed as 'aresult' ofthe discoveryof the phenomenon thatfthemajor'cause of troublein analyzing such substances as 'alcohol,'etc., istheadsorption of such substances on the'suria'ces'of the 'apparatusintermediate the sample leakand the ionization chamber. 'Heretofore"it has been'as- 'isum ed that all'ofthe surfaces of the apparatus have, shared equally in objectionable adsorption.

If "such were the case the provision of asample leak 'in' or adjacent tothe 'ion'izationchamber wouldcor'r'ectfthe errorfto only a relativelysmall extent. However, byfreason of the 'factthat the major portion of the harmful adsorption takes place intermediate "the "sample" leak and; theion- "izati'on chamber, the provisionof leak apparatus absolute minimum produces a disproportionately which reduces the intermediate "surfaces to' an large beneficialfeifect. Thus using'the'leakof I the invention I'am able tomake rapidand accurate analyses of alcohols, -aldehy'des, ketones,

'and'o'ther oxygenated-substances.

assets:

' of the diskremote from the chamber.

2. A sample inlet system for an evacuated chamber having an inlet nipple which comprises a tube having a longitudinal boretherethrough and adapted to be fitted to thefnipplajand a perforated metal foil disk ailixed transversely 'in the bore of the tube adjacent the end thereof nearest the evacuated chamber, the diameter of the perforations in the disk being approximately the mean free path of the sample molecules at the pressure subsisting in the tube on the side of the disk remote from the chamber.

3. A sample inlet system for an evacuated chamber having an inlet nipple which comprises a glass tube having a longitudinal bore therethrough one end of the tube being adapted to slip over the inlet nipple, and a perforated metal foil sealed in the tube across the bore therein and adjacent said one end of the tube.

4. A sample inlet leak for an evacuated chamber having an inlet nipple which comprises a thick walled glass tube one end of which is adapted to slip over the inlet nipple, and a perforated metal foil disk sealed in the tube transversely and across the passageway therein and adjacent said end thereof adapted to slip over the inlet nipple.

5. A sample inlet leak in accordance with claim 4 wherein the metal foil disk is gold foil and the diameter of the perforations therein is less than the mean free path of the sample molecules on the side of the leak remote from the evacuated chamber.

6. A sample inlet system for an evacuated chamber having an inlet nipple which comprises a first metal tube insertable in said nipple and having a bore therethrough, one end of said bore being of larger diameter than the other and forming a shoulder therewith, a perforated metal foil disk disposed across the bore, and a second metal tube insertable in said one end of the bore of said first tube to hold the foil disk against the shoulder.

7. A sample inlet system for an evacuated chamber having an inlet nipple which comprises a first metal tube insertable in said nipple and having a bore therethrough, one end of said bore being of larger diameter than the other and forming a shoulder therewith in the tube, a perforated metal foil disk disposed across the bore, a second metal tube insertable in said one end of the bore of said first tube to hold the foil disk against the shoulder, said second tube having a bore of substantially the same diameter as the smaller section of the bore in the first tube.

8. A sample inlet system for an evacuated chamber having an inlet nipple which comprises a cylindrical metal body insertable in said nipple and of such size as to be held snugly therein, a longitudinal bore in said body having a first section and a second section, the second section being generally shorter in length than the first section and being of a larger diameter than the first section so as to form a shoulder within the body separating the two sections of the bore, a

perforated metal foil disk disposed across the bore, and a metal sleeve insertable in the second section of the bore of the body to hold the foil .disk against the shoulder, the metal sleeve having a bore of substantially the same diameter as the first section of the bore in the body.

.9. A sample leak system in accordance with claim 8' wherein the diameter of the perforations in the metal foil is less than the mean free path 1 of the sample molecules at the pressure subsisting at the side of the leak remote from the ionization chamber.

10. A sample leak system in accordance with claim 8 wherein the diameter of the perforations in the metal foil disk is less than t; the mean free path of the sample molecules at the pressure subsisting at the side of the leak remote from the evacuated chamber.

11. In a mass spectrometer having an ionization chamber and an inlet nipple for receiving a sample to be analyzed into the ionization chamber, the improvement which comprises a tube having a longitudinal bore therethrough and adapted to be fitted to the nipple for passage of gas therebetween, and a perforated disk affixed transversely in the bore of the tube adjacent the end thereof nearest the ionization chamber.

12. In a mass spectrometer having an ionization chamber and an inlet nipple for receiving a sample to be analyzed into the ionization chamber, the improvement which comprises a tube having a longitudinal bore therethrough and adapted to be fitted to the nipple for passage of gas therebetween, and a perforated metal foil disk aifixed transversely in the bore of the tube adjacent the end thereof nearest the chamber, the diameter of the perforations in the disk being approximately the mean free path of the sample molecules at pressure subsisting in the tube at the inlet side of the disk.

13. In a mass spectrometer the combination which comprises an ionization chamber, an inlet nipple opening into the ionization chamber, and a capillary leak removably disposed within the nipple for admitting a sample of gas substantially directly into the ionization chamber.

14. In a mass spectrometer the combination which comprises an ionization chamber, an inlet nipple opening into the ionization chamber, and a metal leak removably disposed within the nipple for admitting a sample of gas substantially directly into the ionization chamber, the metal leak comprising a plurality of capillary leaks.

15. In a mass spectrometer the combination which comprises an ionization chamber, and a capillary leak for admitting a sample of gas substantially directly into the ionization chamber, the solid surfaces between the leak and the ionization chamber to which the gas sample is exposed being substantially all metal.

16. A sample inlet system for flowing a gas sample from a sample source into an evacuated chamber having an inlet nipple, which comprises a tube having a longitudinal bore therethrough and adapted to be fitted to the nipple, and a perforated metal foil disk afixed transversely in the bore of the tube adjacent the end thereof nearest the evacuated chamber, the diameter of the perforations in the disk being smaller than the mean free path of the sample molecules at the pressure subsisting in the sample source.

17. A sample inlet system for flowing a gas sample from a sample source into an evacuated chamber having an inlet nipple, which comprises the mean free path of thesample molecules at thepressure' subsisting in the'sample source.

18. "In the analysis by mass spectrometry Y of--a gaseous mixture containing an oxygenated organic "compound" involving the introduction of a'sample of the" gaseous" mixture into an evacuated ionization chamber through a nipple 'opening into'the chamber, the improvement which comprises reducinglthepressure ofrthe sample to the chamber-pressure within "the inlet nipple and at a point spaced from the outer endpfrthe' J-i-nIet nipple.

CLIFFORD BERRY.

-,REFERENCES CITED 7 Dhe,followingrreferences are of record in the ,fileyof this. patent: v

1 UNITED' STA'I'ES PATENTS ,Number Name iDate 2,136,844 Fair,et,a.1.- Nov. .15 1938 2,387,786 "Washburn .Oct; 39, 1945 2,490,278 Nier Dec; 6,1949

OTHER-REFERENCES vHonig; 'Journal of Applied-Physics, vNovember, 19415, volume:16;"p ges '646+65,4. 

